High impact information on SIS2

• The yeast Ppz protein phosphatases and the Hal3p inhibitory subunit are important determinants of salt tolerance, cell wall integrity and cell cycle progression [1].
• Therefore, Hal3p might modulate diverse physiological functions of the Ppz1 phosphatase, such as salt stress tolerance and cell cycle progression, by acting as a inhibitory subunit [2].
• Previous work has shown that yeast cells deficient in Ppz1 protein phosphatase or overexpressing Hal3p, a novel regulatory protein of unknown function, exhibit increased resistance to sodium and lithium, whereas cells lacking Hal3p display increased sensitivity [2].
• These results are consistent with a model in which the Ppz1-Hal3 interaction is a sensor of intracellular pH that modulates H+ and K+ homeostasis through the regulation of Trk1p activity [3].
• We show here that the described effects of HAL3/SIS2 on sit4 mutants are fully mediated by the Ppz1 phosphatase [4].

Biological context of SIS2

• High-copy-number expression of HAL3/SIS2 has been reported to improve cell growth and to increase expression of G1 cyclins in sit4 phosphatase mutants [4].
• The Saccharomyces cerevisiae SIS2 gene was identified by its ability, when present on a high copy number plasmid, to increase dramatically the growth rate of sit4 mutants [5].
• These results reveal a role for Ppz1 as a regulatory component of the yeast cell cycle, reinforce the notion that Hal3/Sis2 serves as a negative modulator of the biological functions of Ppz1, and indicate that the Sit4 and Ppz1 Ser/Thr phosphatases play opposite roles in control of the G1/S transition [4].
• The ability of different genes to suppress sit4 phenotypes (such as temperature sensitivity and growth on non-fermentable carbon sources) or to mimic the functions of Hal3 was evaluated [6].
• The activity of CtHAL3 was equivalent to that of an open reading frame (YKL088w) identified by genome sequencing of S. cerevisiae and with homology to HAL3 [7].

Regulatory relationships of SIS2

• Neither ENA1 nor HAL3 gene expression was positively regulated by Imp2p [8].

Other interactions of SIS2

• These results indicate that, besides its role as Ppz1 inhibitory subunit, Vhs3 (and probably Hal3) might have important Ppz-independent functions [9].
• The salt-tolerance gene HAL3 from Saccharomyces cerevisiae encodes a novel regulatory protein (Hal3p) which modulates the expression of the ENA1 sodium-extrusion ATPase (Ferrando et al., Mol. Cell. Biol. vol. 15, 1995, pp. 5470-5481) [7].
• We reported that, in the yeast Saccharomyces cerevisiae, overexpression of the Ptc3p isoform resulted in increased lithium tolerance in the hypersensitive hal3 background [10].
• Deletion of PTC1 in a hal3 background did not exacerbate the halosensitive phenotype of the hal3 strain [10].
• Taken together, these observations suggest that calcineurin, Hal3, and Lic4 cooperatively regulate the response of yeast cells to cation stress [11].

References